1. Field of the Invention
The present invention relates to an improvement of a sync frame (synchronous frame) used in an information storage medium such as an optical disc or the like. More particularly, the present invention relates to an information storage medium, an information recording method, an information reproduction method, and an information reproduction apparatus, which are based on an information recording format (sync frame structure) using the improved sync frame. The present invention is compatible to next-generation optical discs (next-generation DVD-ROM standard, next-generation DVD-R standard, next-generation DVD-RAM standard, and the like).
2. Description of the Related Art
On recordable optical discs, preformat information is recorded in advance. When an optical disc apparatus records data on such optical disc, it detects the preformat information, and determines the recording position of data with reference to the detected information.
Normally, a recording track, which is spirally formed on an optical disc, is segmented into address segments each having a predetermined length. Addresses indicating locations are assigned to these segments, and are written as preformat data.
In a CLV optical disc with a constant recording linear density, the address segment lengths are equal to each other. If the number of address segments is too large, a seek time required to seek address information by random access is prolonged. For this reason, a length that can assign 10 to several 10 address segments per round is selected.
As a method of giving the preformat data, the preformat data may be formed as prepits at the head of each segment. However, with this method, that portion cannot be used as a data area. Hence, recent recordable media adopt a method of recording format information by superposing it on a data recording track as a wobble signal which is formed by wobbling grooves.
Upon recording format information as a wobble signal, modulation such as phase inversion, frequency change, or the like is applied. +R adopts such scheme. On the other hand, DVD-R adopts a method of recording format information by discretely forming prepits on lands between neighboring grooves.
As data to be recorded, error correction codes are generated based on original data, and are segmented into smaller sync frames to obtain recording data. For example, in DVD (Digital Versatile Disc), error correction code blocks (ECC blocks) are modulated, and sync codes are appended at given intervals to generate a plurality of sync frames. These plurality of sync frames are used as recording data.
As references related to the present invention, Japanese Patent No. 2,786,810 (reference 1) and Jpn. Pat. Appln. KOKAI Publication No. 2002-373472 (reference 2) are known. Reference 1 describes the technical contents related to sync codes used in existing DVD. This reference 1 corresponds to U.S. Pat. No. 5,587,991. Reference 2 describes a method of determining a reproduction position in a sector based on the allocation order of a plurality of (three) sync codes.
The existing DVD standard that adopts sync codes associated with the contents described in reference 1 specifies 32 different sync codes. In order to detect such sync code position by an information reproduction apparatus or information recording/reproduction apparatus, round-robin pattern matching detection is made between reproduction data reproduced from an information storage medium and these 32 different patterns. Since this sync code position detection takes a lot of trouble, a sync code detection circuit is complicated, thus increasing the price of an information reproduction apparatus or information recording/reproduction apparatus.
Also, since a sync code detection algorithm is complicated (due to the presence of 32 different sync codes), the detection reliability is low. In addition, since a code length (the number of bits of a whole sync code) which is to undergo pattern matching is as large as 32 bits, defects on an information storage medium further deteriorate the reliability of sync code position detection.
When the reproduction pattern of a sync code is erroneously detected due to defects or the like on an information storage medium, information immediately after that pattern causes an error, thus posing another problem.
Reference 2 describes a method of determining a reproduction position in a sector based on the allocation order of a plurality of (three) sync codes. However, if one of the plurality of sync code values is erroneously detected upon reproduction due to defects or the like on an information storage medium, the intra-ECC block position of subsequent information is detected while being shifted. Then, the error correction performance of the whole ECC block largely impairs. However, reference 2 does not have any description about measures against detection errors of sync codes.